Efforts for the coming year will involve: (a) the effect of selected antibiotics on the formation of membrane lipoteichoic acid in an L-form of Streptococcus pyogenes and (b) the necessity of the membrane lipid of lipoteichoic acid, glycerophosphoryl diglucosyl diglyceride, for survival of this L-form. Also, isotope (C14) studies will begin in order to determine the source of three new, saturated, long chain fatty acids (greater than 30 percent of the total fatty acid content) appearing in the membrane of Mycoplasma pneumoniae after its growth in the presence of a shorter but ubiquitous saturated fatty acid found in nature. The purpose of this study is to elucidate the role of these fatty acids in this mycoplasma's increased resistance to erythromycin, but decreased hydrogen peroxide production. BIBLIOGRAPHIC REFERENCES: Leon, O., and Panos, C. "Adaptation of an Osmotically Fragile L-Form of Streptococcus pyogenes to Physiological Osmotic Conditions and its ability to Destroy Human Heart Cells in Tissue Culture" Infection and Immunity 13, 252-262 (1976).